Electromagnetic device



QW-mwa ELECTROMAGNETIC DEV' May 5. 3942.

ICE

Filed June 2, 195? lm/entof: Franz Kfautwi by Han/7 C y I i5 Attorney.

Patented May 5, 1194.2

' ELECTBOMAGNETIC DEVICE Franz Krautwig, Berlin-Steglitz, Germnm assignor to General Electric cmpany, a corporation of New York Application In 8 Claims.

My invention relates to improvements in electromagnetic devices for use in alternating current circuits und more particularly electromagnetic devices, such as relays, having c movable armature whose movement is dependent on a single-phase alternating current quantity und which must he maintained in a. deuite position independently ci. the variation 'with respect to time ci the instantaneous velue ci quent-ity.

Some :magnetic relays, such ici' exemple as voltage responsive re cys, are energized icy u sin gle alternating voltage normally to rheintcin the movable armature or" the relay in c. predetermined contact controlling position ir-om which it is to he moved e dilerent contact controlling position cri the occurrence oi c. predetermined decree-se in voltage. li the change in position is desired with a small decrease in voltage, then because ci lack of uniiorinity in pull in consequence oi the cyclic vuriution ci the voltiE age, e leise response of the relay they occur.

Thus it is well known to control muny groups of lamps, wetterL-heoters, etc. hy reduction ci the potentiel in alternating current systemsn may he accomplished by a plurality ci operations of a. circuit "oreeiier, each operation consisting of an opening and a closing oi the circuit to he controlled. .Each operaticnhas o. very short cluretion and eppeers the system es a.A momentary lowering;- oi" the voltage. The apparatus to be controlled comprises a relay responsive to the lowering of the voltage end it is well understood that euch relug? should release its armature in response to the seme voltage decreesc. For purpose it is requisite that the resultant magnetic effect exerted on the armature be substantially independent ci the variation with respect to time oi' the instantaneous value of the alternating current quantity energizing the relay. This can he attained, for exemple, by energizing the armature in dependence on two alternating flux@ suitably displaced in phase.

In some distance relays, particularly those oi the impedance type in which c restraining eiect, such as o force er torque dependent on voltage, is opposed to on operating eect, such as a force or torque dependent on current, the mere cyclic variation of the voltage with respect to time may result in such a decrease in the restraining ehect es to cause a false operation of the relay particularly li a high degree of sensitivlty is desired. In other words, because oi the phase angle variation between the current and the voltage, the relay tends to respond to the instantaneous ratio of the voltage and the cures which are June 2, 1939, Serial Germany June 3, 1938 (ci. its- 3ssl 5 lll rent and not the ratio of the root meen square values" of these two comntltiesl s .s is desired. uiilso, es is well known in alternating current and voltage relays, the lack'of uniiormity'in attractive eiort on the armature due to" the cyclic variation in the current or voltage results in noise or hum ond undesirable weer et the parts;

Various expediente heve been proposed 'to eliminate troubles attendent on the luck ci uniioim ity in magnetic attractive eort due to the cyclic verioticn of the alternating current quantity whereby to maintain the .stability ci the armature position throughout such veristion. Among other things, these .ipedients lieve included the use of c. plurality o windings each energized Toy the alternating current quentityih cuestion and one or more phase displacing means connected in circuit with the windings und so proportioned as to provide a. reasonably uniform ei'iect throughout the cyclic variation ci the alternating current quantity. Such ext-rs chase displecEl lng items as condensers, resistors, etc., :not only increase cost but also consume switchboard space. Also, in general, the :more itenicoi equipment, the more opportunities' ior oresirdown and failure to operate propcrlyot the critical time.

.lu accordance with my inventlon l provide en electromagnetic device which hes e movable armature und which can loe energized hy -a sincle alternating current' quantity whos-e cyclic 'variation does not materially shoot the stability ci the armature position. Moreover, in accordence with my invention, I provide an improved electromagnetic device in which this stability of position throughout the cyclic variation of the alternating current quantity is simply and eco nornicollg,y achieved within the device itself end not by extraneous elements, such es condensers, resistors, and the like. of my invention will hereinafter appear in more detail.

My invention will be hotter understood lirom the following description when considered in connecton with the accompanying sheet oi drawings, and its scope will be pointed out in the appended claims.

In the accompanying drawing Figs. l end 2 illustrate diegrammatically for the purpose of leading up to a better understanding ci my in vention electromagnetic devices which have been proposed for maintaining .the armature position- :lng effect constant during the cyclic variation of an alternating current quantity; Fig. 3 illustrates-diagrammatlcally an electromagnetic device cn which the analysisof the `theory of ac-' These and other objectsv non of my invention is based; rig; 4 illustrates diagrammatically an electromagnetic device em'- parts proporbodying my invention with` the tioned in accordance withspeciiic assumptions; Fig. 5 is-a diagram-of curves illustrating flux relations in apparatus embodying my invention:A

aasaoos instantaneousvalues of the iluxes in the legs I, 2

thick black lines in order to`simplify the llustrations, and the fulcrums or pivotal supports are indicated by arrow hea@ and small circles.

Referring now to Fig. 1. the iiux entering the amature 1 at the pivotal support on the core leg l, in consequence of the energization of the winding 8 by an alternating current quantity, .is divided into two fluxes 4whieh'venter and leave the armature by way of the core legs `2 and 3. Thesetwo fluxes are dephased relatively to each other. The phase displacement is obtained'in this case by providing the core leg 3 with a shortcircuited winding 6. This structure presents the advantage of being' cheap but is, on the other hand, disadvantageous in thatit requires-alphase displacement of 90 in' order to maintain the resultant magnetic turning moment or torque acting on the armature constant. Such a large phase displacement cannot be obtained with a A short-circuited winding. The result obtained on the arrangement shown in Fig.l

-the whole is that 1 is not suited for the manufacture of a potential relay which can fulfill the requirements of a control of the herein set forth.

Theserequirements are, however, satisfied by the arrangement shown in Fig. 2 by which it is possible to obtain a phase displacement of 90 between the two iiuxes in the core legs 2 and 3 but only in connection with suitable auxiliary phase displacing means, suchas resistances R1, Re

and a condenser Cb in circuit with energizing windings E; and Ea, if the resultant magnetic turning moment acting on the armature is to be maintained constant.

In arrangements such as those illustrated in Figs. l and 2 Whereinthe magnetic iiux traverses and 3 are f1, fz, fs, and the amplitudes of the flux waves are F1,Fz Fa, then ai, a2,` a3 design.

'Also' f1+fz+fa=0. since the algebraic sum of the iuxes entering and leaving the armature at any instant must be zero in accordance with Kirchois laws as adapted to ilux`ilow. Accordingly,

as shown graphically in Fig. 5.

Also

,p is. the angular velocity of the flux vectors in radians per second and is the angle by which If the resultant torque D on the armature l is to be substantially independent of the cyclicvariation of the alternating current quantity which energizes the winding 8, then the coeiiicients of both the sin 2pt and the cos Zpt terms in Equation 3 must equal O as expressed below: 1/(a1aa)li`32 sin 2+a1FzF sin =0 which by transformation to functions oi the single angle may beexpressed as the magnet armature at the pivotal support thereof, it is likely that the magnetic resistance of the support and also the response of the' relay will vary in the course of time by reason of the wear and tear. In order to obviate this, it has been suggested to arrange the pivot 9 for the armature out'side of the magnetic core, as shown 1I1Fig.3. y

In accordance with my invention, I so proportion the distances di, da, da of the magnetic centers of gravity ofthe three alternating iluxes entering and 'leaving the armature by way of the -core legs I, 2. and 3, respectively,.as to obtain a 'substantially constant resultant magnetic turn-.

ing moment acting upon the armature, with a phase displacement between the two iiuxes in the core legs 2 and 3, respectively, which is less than 90. A phase displacement4 less than 90 can readily be obtained with the aid of a shortthe resultant magnetic turning moment relatively to the armature fulcrum or pivot 9 is D, the

gives: y

F2 Erl' Us F37-- ari-0a The Equations 6 and 7 give the phase displacement and rthel ilux ratio in dependence on the .tive pole fluxes f1, fz,

.distances 'of the three magnetic centers'of gravity as involved in the constants ai, az, a: whichfcan be expressed in terms of the distances di, dz, da, since the torques D1,D2,"Ds due to the respecf: may be written as follows and 7 can be expressed in terms of di. dz. da, as follows:

zi l ws onderdaan (9) Consequently for di=0, that is to say, for arrangements according to Figs. 1 and 2, cos would be equal to zero and accordingly, 90, a condition impossible to obtain with a shading winding alone. But if d1 is not zero, it is possible to accomplish the desired action with phase angles less than 90, which can readilybe obtained with short-circuitingrings. In this case it is immaterial which of the two iluxes Fn and Fa is leading or lagging. Since El F a depend solely on the relative values linear increases of all dimensions do and cos f di, da, da,

'not produce a variation in the resultant magnetic effect. In order to obtain this eilect, lthe two Equations 8 must be satisfied by suitable proportioning of the determining quantities. This can be attained, for example, by adjustment of d1 (horizontal displacement of the amature fulcrum).'

Referring now to Fig. 6, T1, T: and T3 are' curves showing the values ofthe-torques exerted on the armature in consequence of the attractions due to the uxes f1, fr, and fa, illustrated by wave forms in Fig. 5. D is the curve of the algebraic sum of the torques Ti, T: and Ta or, in other words, the difference between T1 and the sum of Ta and Ta. Since D is to be substantially independent of the cyclic variation of the applied alternating current electric quantity when the amature is in a predetermined position. it appears as a straight line whose distance above the zero axis depends on the eiiectivevvalue of the quantity1 Fig. t illustrates my invention in a speciiic embodiment which is based on the foregoing analysis and in which, for examples 1=0.5 (the armature fulcrum lies between the legs i and 2) ds=2i.rk and daf-3.- Then according to the Equation il: cos -0.258, :75 (attainable with a short-circuted winding) Fa The contact E serves for repositioning the dropped armature.,

I; claim:

l. An. electromagnetic device comprising an armature a coopcr-atingy magnetic, memr presenting at least three pole faces to said amature, winding ,means on said member adapted when energized from a, single-phase source of alternating current to establish alternating fluxes in the pole faces of said member and in said armature. short-)circuited winding means on said magnetic member for eiecting a phase displacement between at least two of said fluxes, and meansl supporting said armature intermediate one of said pole faces and the other pole faces for angular movement so positioned relatively to said pole faces that the resultant torque eiIect on the armature due to the attractions between the respective pole faces and the armature when the armature is in a predetermined position and said winding means is energized from a single-phase source of alternating current is substantially constamtA as long as the eective value of said current is substantially constant'.

2. An electromagnetic device comprising an armature, a cooperating magnetic member having three polar projections directed towards said armature, winding means on said member adapted when energized from a single-phase source of alternating current to establish alternating fluxes in said projections' and said armature, shortcircuited winding means on one of said projec- 0 tions for eiecting a predetermined phase displacement between at least two of said uxes,

and a pivotal support for said armature so positioned intermediatelthe third o1 said polar projections and said two polar projections that the resultant torqueeii'ect on the armature due to the attractions between the respective polar projections and the armature when the armature is in a predetermined position land said winding means is energized from a single-phase source of alternating current is substantially independent of the cyclic variation of the current.

3. An electromagnetic device comprising an armature, a cooperating magnetic member having three legs presenting pole faces to said armature,

5 winding means on one outside leg of said member adapted when energizedA from a single-phase source of alternating current to establish alternating vfluxes in the legs of said member and in said armature, short-circuited winding means on 40 the other outside leg of said member for effecting a predetermined phase displacement between the iiuxes in said other outside leg and the leg intermediate the two outside legs. and a pivotal support or said armature between said intermediate leg and said one outside leg so positioned relatively to the pole faces of said legs that the resultant torque of the attractive elects on the armature is substantially independent of the cyclic variation of the alternating current quantity energizing said winding means whenthe armature is in a predetermined position.

4. An electromagnetic device comprising an armature, a cooperating magnetic member presenting three pole faces to said amature, winding means on said member adapted when energized from a single-phase source of alternating current to establish uxes fr, f2 and fa having amplitudes F1, Fn and F3 in the poles oi said member and the armature, the algebraic sum of the fluxes f1, la and fs entering and leaving the armature at any instant being substantially zero, short-circuited winding means on said member for effecting a phase displacement d between the uxes fz and fa, and a pivotal support for said armature so positioned at distances di, da and da, respectively, from the centers of magnetic attraction of said pole faces and relatively to said phase displacement and said flux amplitudes F2 and Fa that cos (d1-l- 2)0111 da) n and agende Fs (dri-dal polarV projections uxes f1, fraud fs,

5'. An electromagnetic device comprising an armature, a cooperating'magnetic member having three polar projections directed towards said armature, winding means on said member adapted when, energized from a single-phase source o1' alternating current to establish in lsaid three respectively, which have amplitudes F1, Fz vand F y3, the a1- gebraic'sum' of the fluxes f1, fz and fa entering and leaving the armature at any instant beingsubstantially zero, short-#circuited winding means associated with .one ofsaid polar projections for effecting a predetermined phase ydisplacement between theuxesffzfand fa'. and avpivotal support for said armature intermediate the polar projections inwhich theuxes f1 and fs occur so positioned atdistances di, d2 and da, respectively; from the centers of magnetic attraction of said polar projections and relatively to said phase displacement and'said flux `amplitudes F2 and F3 that and f` 6. An electromagnetic device comprising yan armature, a cooperating magnetic member having.

three polar projections directed towards said armature, winding means on said member adapted when energized from a single-phase source of alternating current to establish in said three polar projections fluxes f1,fz and f3, respectively, which have amplitudes F1, F2 and F3 the subnumbers l, 2 and 3, respectively, indicating the order of said phase displacement F2 and Fs that cos dl and ,Y

goeder Fa (drt-d 7. An electromagnetic device comprising anarmature, a cooperating magnetic member presenting at least three pole faces' to said armature,

winding means onv saidtmember adapted when energized by a single-phase alternating current f positioned relatively toA saidA the respective pole faces and Aof said memberiand in to establish alternatingiiuires` in the pole faces said armature, means comprising a short-circuited4 winding for effecting -a phase displacement between at least two of said fluxes, and means intermediate one'of said pole facesand thevother two of said pole faces supporting said armature for angular movement so pole faces that the resultant torque effect of the attractions between v the armature is ina predetermined position and polar projections in series, the algebraicsum of the iluxes f1, fz -and'fa entering and leaving the armature at any instant being substantially zero, short-circuited winding means associated with the polar projection energized by the flux fs for effecting a' predetermined phase displacement between the fluxes f2' and f3, and a pivotal support for said armature intermediate the polar projections in which the uxes f1 and fr occur so positioned at distances di, d2 and da, respectively, from the centers of magnetic attraction of said polar projections and relatively to said said Winding means is energized by a single-phase alternating current is substantially independent of the cyclic variation of the current. v

8. An alternating current electromagnetic device comprising an armature, a cooperating magnetic member havingV at least three pole facesI arranged adjacent -said armature so that the iiux passing between oneof `-said pole faces and the armature is the sum of the fluxes passing between the other faces and ing -on said member arranged when energized by a singlenphase alternating current to magnetize the member, means for effecting a. predetermined phase displacement between the fluxes in said other pole faces, and means intermediate said one pole 'face vand the other pole faces supporting said armature for angular movement characterized by the fact that said 'pole faces are so arranged relatively to each other and4 to said supporting means that produced by the flux on said armature is substantially constant in a, predetermined direction when the armature is in a predetermined position and said winding is energized by a single-phase alternatlng current having a constant effective value.

FRANZ KRAUTWIG.

p and said iiux amplitudesl the armature when -the armature, a win'dthe resultant torque eiect y 

